1. Field of the Invention
The present invention relates to a molded motor provided with: a stator; a rotor rotatably disposed inside the stator; and a molded main body which covers the stator.
2. Description of the Related Art
FIG. 4 is a cross-section of a conventional molded motor, FIG. 5 is a front elevation of the stator core of the molded motor in Fig.4 and this molded motor is provided with: a stator 1; a rotor 2 rotatably disposed inside the stator 1; bearings 3 disposed at both ends of the rotor 2 to support the rotor 2 so that it can rotate freely; and a molded main body 4 composed of polyphenylene sulfide resin which covers the stator 1.
The stator 1 is provided with: a stator core 6 laminated from a plurality of layers of cold-rolled steel plate 5, which is a magnetic plate; stator coils 8 composed of lead wires wound around tooth portions 12 of the stator core 6; a first guide 9 and second guide 10 which fit into the stator core 6 from the top and bottom respectively to insulate between the stator coils 8 and the stator core 6; and a terminal 11 fixed by heat crimping to the second guide 10 and connected to the stator coils 8.
The rotor 2 is provided with: a shaft 13 supported at both ends by the bearings 3 so that it can rotate freely; and magnets 14 fixed to the shaft 13 with adhesive, arranged with alternating north-seeking (N) poles and south-seeking (S) poles.
The molded main body 4 has: a connector portion 15; flange portions 17 integrated with bushes 16 into which bolts (not shown) are inserted; and a receiving portion 19 which receives an annulus 18, which is an inserted body.
The molded motor of the above construction is connected by means of bolts inserted into the bushes 16 to a throttle valve device, which regulates the amount of air delivered to an internal combustion engine.
The throttle valve device is provided with: an annulus 18 which is inserted into the receiving portion 19 of the molded main body 4 and which has an internal gear 20 on its inner wall; a sun gear 21 connected to the shaft 12; a planetary gear (not shown) which engages with the sun gear 21 and the internal gear 20; and a shaft (not shown) which passes through the center of the planetary gear.
In the molded motor of the above construction, an integrated motor main body 22 is formed from the stator 1, the molded main body 4, and a bush 23 as shown in FIGS. 6 and 7, by insertion molding, in which resin is injected into a metal mold in which the stator 1 and the bush 23 have been placed. Then the bearing 3, which is secured to the shaft 13, is inserted into the bush 23, and the motor main body 22 and the rotor 2 are integrated, completing the assembly of the molded motor.
In the molded motor of the above construction, rotating magnetic fields of north-seeking (N) poles and south-seeking (S) poles are generated in the stator core 6 by passing an electric current through the stator coils 8, and the magnets 14 and the shaft 13 secured to the magnets 14 follow this rotating magnetic field and rotate.
The sun gear 21 of the throttle valve device rotates with the rotation of the shaft 13. The planetary gear, which is engaged with the sun gear 21 and the internal gear 20 of the annulus 18, rotates and revolves around the sun gear 21. With the rotation of the planetary gear, a gear (not shown) rotate and the throttle valve (not shown) rotates. The amount of air delivered to the internal combustion engine varies in response to the rotational angle of this throttle valve.
In the conventional molded motor, the motor main body 22 is formed by injecting high-temperature resin into a metal mold, but there is a problem in that cracks form during natural cooling after molding at point A in FIG. 6, for example, due to differences in the coefficient of thermal expansion between the molded main body 4 and the stator core 6. In other words, during natural cooling, the amount of shrinkage in the molded main body 4 is greater than the amount of shrinkage in the stator core 6, and the temperature of the stator coils 8 is also low, so that in the vicinity of the stator coils 8, the molded main body 4 is cooled quickly and hardening of the resin proceeds quickly, leading to problems in that cracks form at point A between the stator coils 8 where hardening is slow.
Also, when the motor main body 22 is stored, there is a problem in that water accumulates at point B in FIG. 6, for example, due to condensation, etc., and the stator core 6 is subject to corrosion.